Reflector



W. J. HARSHAW REFLECTOR Sega. 14, 1943,

Filed April' 50, 1941' Trans/uc en 7 Enamel INVENTOR. 'W /ham J. HGIS/IGUJ A'ITORNEY.

SUI/er Size! Wavelength in Nil/imicrans Patented Sept. 14, 1943 2,329,532; a t Eli-M01031 William 1. Harsha'w, Shaker Heights, on, I!

signer to The Hal'shaw Chemical Company, Eiyria. Ohio, a corporation of Ohio a Application April 30, 1941, Serial No. 391,139

ZClaims. (c1. 88- 105) This invention relates to reflectors and particularly to reflectors of the type wherein relatively high diffuse reflectivity and low'mirror or specular reflectivity, but together aggregating a high total reflectivity, are desired.

Prior to this invention, reflectors coated with pearance are not obtained by' coating bright or' matte silver with clear organiclacquers.

opaque porcelain enamels have been used for obtaining diffuse reflectivity. Theydo reduce specular reflectivity to a small value, but the diffuse reflectivity and the total reflectivity obtainable are not as great as could be desired for a reflector.

An object of thepresent invention is to obtain the advantages of a silver reflector, however with an appearance of extreme whiteness and substantially without the metallic appearance of sil-,

ver, and to overcome in a reflector the wellknown tendency of silver to corrode and discolor when exposed to the atmosphere.

A further object is to provide an illuminating device including a reflector capable of giving a high diflu'se reflectivity coupled witha high total and low specular reflectivity. The present invention ispiimarily concerned j tube interiorly coated with zinc-beryllium siliwith making available for purposa oi illumination a reflector giving a highdifluse reflectivity and a high total reflectivity such reflector including a matte surfaced, (preferably elect'rodepos- The foregoing objections are realized inand "through the structures and procedures herein described and claimed and which structures are illustrated, insofar .as practicable, .inthe accompanyi d wing, in which Fig. l is a diagram matic, view representing a section of a lamp flxture comprising a-reflector and source of light; Fig, Bis an enlarged fragmentary section showing in detail the construction of the reflector; and Fig. 3 is a diagram showing approximately thc'curves traced by a Hardy recording spectrophotometer analyzing the color characteristics of reflectingsurfaces according. to the invention;

matte silver surfaces and opaque vitreous enam surfaces.

In the drawing, the numeral iii indicates generally a sheet. metal reflector element shown in section and associated with a source of light ii. The reflector element It may be elongated and 'the source of light ll may be a fluorescent tube,

for-example, a hot cathode, argon-mercury filled cate. It is to be understood that suitable connections are provided for supp ying suitable current to'the source'of light II, 811 this being conited) coating 0! silver and a coating of transparent vitreous enamel applied over such silver surface. Surprisingly, the metallic appearance of the silver surface is almost completely lost and the impression is one of extreme whiteness; Silver is by far the best metal for the purpose, .being high in'reflectivity both before and after the application of transparent enamel. However, copper and noble metals other than silver'and alloys high in copper or. noble metals or mixtures of one or more metals of the c1assconsistventional' and well known to persons skilled in the art of illumination.

Fig. 2 I have shown an enlarged section of a fragment ofthe reflector ill. As will be clear from the drawing, the silver deposit i2 is applied .over the steel base It and the clear enamel it ing of copper and noble metals can be used with j more or less good results. By the expression noble metals, I mean silver, palladium, platinum and gold. Silver having a mattesuriace gives afar more pleasing appearance after enamel is applied than does highly polished silver, the appearance of whiteness being more pronounced and the residual metallic appearance being almost nil in'the case of the matte surface while still being distinctly perceptible in the case of the polished surface. effects are obscure. If any fllm exists at the interface, it is so thin as not to be apparent upon separating the enamel from the metal surface.

Such separation exhibits an apparently uncoated lass and restores the metallic appearance of the silver. The whiteness and loss of metallic ap- The reasons for these overlies the silver deposit. It is to be understood that the translucent enamel is on the inner surface of the reflector so that the light from the source II will impinge thereon. The outside of the reflector ll may be finished in the same way or may be painted, plated, or otherwise finished in any desired manner.

Reflectorelements according to the invention,

may, as indicated, consist of a sheet, .i'errous metal base such as steel which may be'pollshed and silver plated on the polished surface or ml ished, then acid etched or lightly abraded with an abrasive which will leave a matte surface and then silver plated, after thorough cleaning in each case as is customary in plating practice. The ferrous metal base may be of any desired thicknessl The silver plate need not be very thick. Good results may be had, for exampleQby the production of a; deposit of athickness not exceeding 0.00025 of an inch. If the silver deposit is'very thin, e. g. below'.0005-of an inch, it is; well to deposit the same on a matte or satin flnish steel or other base metal. It is preferable to have from 0.001 to 0.005 of an inch of silver, however. The silver platingbath should be such as to produce a matte deposit, since otherwise it will be desirable (although not absolutely necessary) to etch or otherwise treat the deposit to form a matte finish, Such a procedure would result in loss of silver and require an extra operation. If the silver is deposited brightor buffed, the specular reflectivity is increased while the diffuse reflectivity is lowered. A polished silver deposit exhibits, before sounding, a low diiiuse reflectivity and a high specular reflectivity, while be noted that they are approximate copies of charts which were made on a Hardy recording spectrophotometer which rejects most of the specular reflection from the sample. All samples were done on the same machine. In the case of reflectors according to this invention and in the case of. opaque porcelain enamels as well, the specular reflectance is only a few percent (probably not exceeding and does not greatly influence the comparison. In the curves, ordinates represent percentage reflectance (MgO: 100%), a small part of the specular reflection be- 0 ing rejected by the instrument, and abscissae after enameling it exhibits a high difluse reflectivity but not as high as in the case of a matte surface. Also, in that case, the metallic appear-' ance is not entirely st. 7 It is possible, of course, to make use of a sitver reflector element insteadof a silver plated one. However, this is hardly to be'considered a practical possibility except for very expensive flxtures in view of the cost of silver. sheet silver be used, the surface to be enameled should be lightly etched or otherwise treated to give the desired matte or satin flnish.

The thickness of the transparent enamel or glaze is not critical. It should .be thick enough to afford adequate protection of the silver against corrosion (to which silver is peculiarly susceptible when unprotected) and desirably may be from 0.005 to-0.0l0 of an inch in thickness.

The silver deposit may be produced from any conventional silver plating both, such for example as the following:

Partsbyweight Borax 4.0 Quartz 29. Soda ash 4.7 NaNO: 4.2

K100: 2.0- Red lead 42.0 AszOa 1.0 BbsO: 1.0

These enamels are applied in accordance with usual ractice, being melted on the metal base at a temperature approximating the minimum for melting to a homogeneous translucent coating.

Following the indicated procedure, I am able to produce reflectors characterized by an average diifuse reflectivity over the visible spectrum of the order of 80% to 90% (MgO=100%) and varying but little at the different wave lengths.

In Fig. 3 are shown some spectrophotometer charts illustrating the effects obtained; In connection with'the curves shown inFig. 3,- it is to represent the wave length of the light in millimicrons. r The curve 2 was taken from a sample consisting of a matte silver deposit about .002 to .003 of an inch thick on polished steel, not yet enameled,

' while the curve 3 was taken from a sample con- ShOllld AgNOa 3.2to4.0 oz./gal. NaCN 5 to6 ozJKal. KNO: 15 oz./gal.. Hi--..---; To make one gallon Current density 5 amps/sq. ft.

sisting of a matte silver deposit on matte surfaced steel, not yet enameled.

The curve I wastaken from a sample like 2 except that the mattesilver surface was covered by transparent vitreous enamel. The curve 4 was'taken from a sample'like 3 except that the matte silver deposit was covered by transparent vitreous enamel.

The curve I was taken from a sample consisting of sheet steel coated by-a white porcelain enamel prepared from a commercial "superopaque" antimony frit opacifled at the mill with 6% of tin oxide. The curve I was taken from a sample similar to I but opacifled with a commercial tin oxide substitute sold under the trade name Uveriter Curves I and I are included merely for the purpose of comparing the reflectivity of reflectors according to the present invention with reflectors coated with highly opaque porcelain enamels. (These are very high reflectance opaque porcelain enamels.)

From the foregoing, it will be obvious that I have provided a reflector construction which is departing from the nature of the invention, within the scope of what is-hereinafter claimed.

What is claimed is: 1. A reflector comprising a base, asilver coating on said base, the same having a thickness from .00025 and .005 of an inch and having a matte surface, and an adherent layer of translucent vitreous enamel covering said silver coating, said reflector being capable of exhibiting an averagediifusive reflectance in excess of 80% [2, A reflector comprising a metallic base,- a

silver electrodeposit adherent to said base, having a thickness from .00025 to .005 of an inch and having a matte surface and a coating of translucent vitreous enamel covering said silver elec-' trodeposit, said reflector being capable of exhibiting an average diffusive reflectance in excess of as determined by the Hardy recording spectrophotometer, magnesium oxide being taken WIILIAM' J. mmsrmw. 

